Pushrod's aren't really made for any specific engine... they are typically custom made for the size and craft they are being used in. You get the types of ends you need for your situation and there are more than one way to make them. The ends can be made several ways including simple Z bends of just wire up to the metal clevis's that go on the end of a threaded rod. The rods between the ends can be simple square or round hardwood stock to carbon fiber to a long flexible tube ( typically in a sleeve ) to just the wire being used to create the Z bends out of. In all cases, they are all custom fit to the specific model being used on. Those are just a few of the options used to make a pushrod, the limits are only bound by your own imagination.
Where I'd start... is with what the original model had originally or had recommended if it was built from plans. If that is unknown, then you have to design one and just source the parts you'd need. Basic rule of thumb for a pushrod is to have them as straight as possible from servo to the control surface ( in this case your throttle arm on the engine ). The more curves and kinks in the pushrod, the more slop you'd see when trying to control the surface you are moving.